As disclosed in WO 2004/083286, the majority of plastic materials for packaging are today based on petroleum. However the fossil resources on the earth are limited. Incineration results in an increase of the greenhouse effect and furthermore these materials are in general not degradable. A sustainable development in the future requires a conversion to the use of renewable raw materials.
In many food packaging applications it is important to protect the food from oxygen as oxidation of aroma compounds, fatty compounds and vitamins due to the ingress of oxygen, reduces the quality and/or the flavor of the product. This can be done by using a barrier material, which has low permeability to oxygen. Furthermore, it is desirable that the material is flexible, mechanically resistant, transparent and of low cost. Also other barrier properties, such as aroma barrier and grease barrier can be of great importance.
Hemicelluloses are polysaccharides that are biosynthesized in the majority of plants, where they act as a matrix material present between the cellulose micro fibrils and as a linkage between lignin and cellulose. Hemicelluloses have been commercially used as sweetening agents, thickeners and emulsifiers in food. So far the non-food utilization of hemicelluloses has been very limited. For example, not until WO 2004/083286 have they been suggested to be used commercially for the preparation of polymeric materials for packaging.
As disclosed in WO 2004/083286, films and coatings based on hemicellulose are good oxygen barriers. WO 2004/083286 also describes a method to improve mechanical properties.
Hemicellulose interacts with liquid/moisture and the permeability of oxygen, aroma, and grease increases at high relative humidities. The water solubility of the material is an advantage in coating processes, but can be a draw-back for many packaging applications.
U.S. Pat. No. 5,498,662 and U.S. Pat. No. 5,621,026 and their European counterpart EP 649 870 as well as U.S. Pat. No. 5,897,960 and its counterpart EP 665 263 relate to a moisture resistant gas barrier film and to a process for producing the film, respectively, based on poly(meth)acrylic acid polymer (PMA) and a saccharide, and heat-treatment of the film. The saccharide preferably is a polysaccharide, such as starch. Xylan and arabinoxylan are mentioned, by the way, as heteropolysaccharides composed of only pentose. PMA is based on petroleum.
Further, US 2005/0070703 proposes a method for the production of a moisture resistant, biodegradable polysaccharide-based network by homocrystallization or hetero-crystallization of a mixture of at least one basic polysaccharide and at least one networking polysaccharide.
Thus, there is a need for new biodegradable film-forming compositions, which overcome the abovementioned problems, and which present the desired property of having low permeability to oxygen, grease and/or aroma.